From: B_DAVISON <Bob.Davison@...>
Date: 2000-03-20T15:38:23+00:00
Subject: [ruby-talk:02036] Anonymous and Singleton Classes

I am a Ruby newbie and having some problems getting my mind around certain
aspects of classes, especially anonymous classes and singleton classes.

I composed a nice long mail to you all then realised that I should check the
mail archive first and found the February thread "Singleton Classes".  Now I am
even more confused!

I had just decided that class << obj; ...; end didn't actually create an
anonymous class (even though FAQ 6.6 says it does) and then matz says that it
does.

<code>

class C1
 def to_s
   ">>> C1.to_s"
 end
end

def C1.inherited(subclass)
  print ">>> inherited ", subclass, "\n"  #  never called
end

obj = C1.new
class << obj
  def to_s
    super + " => C2.to_s"
  end
end

print obj, "\n"                   #  >>> C1.to_s => C2.to_s
print obj.type, "\n"              #  hmm, still says C1
print obj.type.id == C1.id, "\n"  #  true, it really is C1

</code>

Well it looks like it does when it comes to calling super() as C1.to_s gets
called.  But obj.type is unchanged and Class.inherited() doesn't get called. So
what is going on?

Actually Class.inherited() doesn't seem to get called when subclassing with
Class.new() either.  Is this a bug?

ruby -v
ruby 1.4.3 (1999-12-08) [i686-cygwin]

<code>

class C1
end

def C1.inherited(subclass)
  print ">>> inherited ", subclass, "\n"
end


class C3 < Class.new(C1)
end

print C3.ancestors.join(", "), "\n"

</code>

outputs:
>>> new subclass C3
C3, #<Class 0lx1208af08>, C1, Object, Kernel


Thanks,
Bob

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